Abstract : Background: Both duration and morphology of the T-wave are regarded important parameters describing repo-larization of the ventricles. Conventionally, T-wave concordance is explained by an inverse relation between the time of depolarization TD and repolarization TR. Little is known about T-wave morphology and TD-TR relations in patients with heart failure. Methods: Electro-anatomic maps were obtained in the left LV and right ventricle RV and in the coronary sinus CS in patients with heart failure with narrow nQRS, n = 8 and wide QRS complex with LBBB, n = 15 and without left bundle branch block non-LBBB, n = 7. TD and TR were determined from the thus acquired electro-grams. Results: In nQRS and non-LBBB patients, TD-TR relations had a slope between 0 and +1, indicating that repolar-ization followed the sequence of depolarization. In LBBB patients, repolarization occurred significantly earlier in the RV than in the LV, fitting with the idea that the discordant T-waves in LBBB are secondary to the abnormal depolarization sequence. However, the slopes of the TD-TR relations in the LV and CS were not significantly different from zero, indicating no major spatial gradient in LV repolarization, despite a considerable gradient in de-polarization. Remarkable was also the large ~100 ms transseptal gradient in repolarization. Values of the slopes of the TD-TR relation overlapped between the three patient groups, despite a difference in T-wave morphology between LBBB all discordant and nQRS patients all flat-biphasic. Conclusions: Discordant T-waves in LBBB patients are explained by interventricular dispersion in repolarization. T-wave morphology is determined by more factors than the TD-TR relation alone.